Wall Square Footage Calculator

Calculate the square footage of the walls in a room from its length, width and ceiling height, minus doors and windows, for paint, drywall, wallpaper or tile.

By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.

Quick answer: To find wall square footage, multiply the room perimeter by the ceiling height, then subtract about 20 sq ft for each door and 15 sq ft for each window. A 12 x 14 ft room with 8 ft ceilings has 416 sq ft of gross wall area and 366 sq ft of wall after deducting one door and two windows.

Results

Wall square footage: 366 sq ft; After deducting 50 sq ft for 1 door and 2 windows
Gross wall area: 416 sq ft; 52 ft perimeter x 8 ft ceiling height, before openings
Long walls (2): 224 sq ft; Each 14 ft x 8 ft, before openings
Short walls (2): 192 sq ft; Each 12 ft x 8 ft, before openings
Perimeter: 52 ft; 2 x (Length + Width), the total length of wall

Wall Square Footage formula

Perimeter = 2 x (Length + Width)
Gross wall area = Perimeter x Ceiling height
Wall square footage = Gross wall area - (Doors x 20) - (Windows x 15)
Ceiling area = Length x Width  (add it when the ceiling is being covered too)

Worked example

An 11 x 13 ft bedroom with 9 ft ceilings, two doors and one window: the perimeter is 2 x (11 + 13) = 48 ft, so the gross wall area is 48 x 9 = 432 sq ft. Deduct 2 x 20 = 40 sq ft for the doors and 15 sq ft for the window: 432 - 55 = 377 sq ft of wall. The two long walls are 2 x 13 x 9 = 234 sq ft and the two short walls are 2 x 11 x 9 = 198 sq ft.

If the ceiling is being painted as well, add 11 x 13 = 143 sq ft, for 520 sq ft of walls plus ceiling.

Quick reference

Wall square footage for common rooms (8 ft ceilings, 1 door, 2 windows)
Room size	Perimeter	Gross wall area	After openings
10 x 10 ft	40 ft	320 sq ft	270 sq ft
10 x 12 ft	44 ft	352 sq ft	302 sq ft
12 x 12 ft	48 ft	384 sq ft	334 sq ft
12 x 14 ft	52 ft	416 sq ft	366 sq ft
12 x 15 ft	54 ft	432 sq ft	382 sq ft
14 x 16 ft	60 ft	480 sq ft	430 sq ft
15 x 20 ft	70 ft	560 sq ft	510 sq ft
20 x 20 ft	80 ft	640 sq ft	590 sq ft

How to measure the walls in a room

Measure the length and width of the floor along the baseboards and the ceiling height in a corner, where the tape can stand straight. For a simple rectangular room, the perimeter times the height is the gross wall area. Rooms with alcoves, closets that open into the room, or a bay window are easier to do wall by wall: measure each wall's length, multiply by the height, and add them up.

Sloped ceilings and stair walls are triangles or trapezoids. Measure the wall at its shortest and tallest points, average the two heights, and multiply by the length. Round up rather than down; a few extra square feet is cheap insurance against running short.

When to deduct doors and windows

For paint, deduct the openings. Twenty square feet per door and 15 per window is close enough for standard sizes, and it keeps you from buying a gallon you do not need. Measure large openings such as patio doors, garage doors and picture windows instead of using the allowance.

For drywall, wallpaper and tile, most estimators skip small openings entirely. The pieces cut out for a window or door are usually waste, not usable stock, so the gross wall area is the better number to buy from. Deduct only openings larger than about 32 sq ft, the size of a full sheet.

Key facts

A standard interior door is 80 in tall and 30 to 36 in wide, about 20 sq ft with its casing.
An average window is counted as 15 sq ft; a picture window or sliding patio door can be 40 sq ft or more, so measure those separately.
Standard ceiling height in US homes is 8 ft; 9 ft ceilings are common on the first floor of newer houses and add 12.5% more wall area.
A 12 x 12 ft room with 8 ft ceilings has 384 sq ft of gross wall area, about 334 sq ft after one door and two windows.
Wall square footage drives most finish estimates: a gallon of paint covers 350 to 400 sq ft and a 4 x 8 sheet of drywall covers 32 sq ft.

Frequently asked questions

How do I calculate the square footage of a wall?

Multiply the wall's length by its height. A 14 ft wall under an 8 ft ceiling is 112 sq ft. For a whole room, multiply the perimeter by the height: a 12 x 14 ft room has a 52 ft perimeter, so 416 sq ft of wall.

Should I subtract doors and windows from wall square footage?

For paint, yes: about 20 sq ft per door and 15 per window, which takes a 12 x 14 ft room from 416 to 366 sq ft. For drywall and wallpaper, most estimators skip small openings because the cutouts end up as waste anyway.

How many square feet of wall are in a 12 x 12 room?

384 sq ft with 8 ft ceilings before openings, or about 334 sq ft after one door and two windows. With 9 ft ceilings the gross area is 432 sq ft.

Does wall square footage include the ceiling?

No. Add length times width if the ceiling is being covered too. A 12 x 14 ft room adds 168 sq ft, for 534 sq ft of walls plus ceiling after openings.

Sources and references

Paint calculator: coverage per gallon and room measurement (Sherwin-Williams)
Paint calculator: room dimensions less doors and windows (Benjamin Moore)
Chapter 3 Building Planning, 2021 IRC (ceiling height, door and window sizes) (ICC)

Next steps for this project

The usual order for a paint & walls project. See all paint & walls calculators.

Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.